1. Field of the Invention
The embodiments disclosed herein relate to compounds that may be useful in organic light emitting diode materials, such as ambipolar hosts for emissive materials of organic light emitting devices.
2. Description of the Related Art
White organic light emitting devices (WOLEDs) have attracted much attention and have been intensively studied due to their potential applications as backlight sources, full color displays, and for general lighting purposes. Among various device configurations to produce white light, devices with a single emissive layer have attracted much attention due to their simplicity of device fabrication and processing. Of the many types of single emissive layer that exist, devices employing phosphorescent materials in combination with proper host materials (all-phosphorescent), and the devices using a blue fluorescent host with a yellow phosphorescent emitter have attracted particular attention. These may be more effective than other types of devices for several reasons. For example, phosphorescent emitters can harvest both singlet and triplet excitons, and may thus have the potential of achieving 100% internal quantum efficiency. Another important consideration is that adding host materials not only may reduce concentration quenching of the emissive materials but may also reduce the overall cost of a device because the emissive materials may be more expensive than host materials. Additionally, fabrication of single layer devices may be much easier and may be more cost effective than multiple layer devices.
Therefore, development of effective host materials is important to improving the efficiency of WOLEDs. It may generally be desirable that a host transport both holes and electrons efficiently at same speed, and have a triplet energy high enough to effectively confine the triplet excitons on the guest molecules. Many host materials may be a mixture of hole-transport material and electron-transport material, which may pose potential problems such as phase separation, aggregation and lack of uniformity, and unequal material degradation. Development of single molecule ambipolar hosts (e.g. a host molecule which may transport both holes and electrons effectively) may provide improvement in these areas.
Synthesis and studies of some ambipolars host used in either single color or white organic light emitting diode (OLED) device applications have been reported. Many of them, however, may have either unbalanced hole-transport and electron-transport properties, or the devices made thereof may have showed only moderate efficiency.